The Bacillus Calmette-Guérin (BCG) vaccine's variable effectiveness against tuberculosis (TB) is attributed to several factors. Firstly, the vaccine is more effective in preventing severe forms of TB in children, such as TB meningitis, rather than pulmonary TB, which is more common in adults. Genetic differences in populations, environmental factors, and variations in the strains of Mycobacterium tuberculosis also influence the vaccine's efficacy. Additionally, the vaccine's effectiveness appears to diminish over time, necessitating further research into booster doses or new vaccines. The complexity of the TB pathogen and the host's immune response further complicates vaccine development and effectiveness.

Antiretroviral therapy (ART) for HIV/AIDS works by targeting various stages of the HIV life cycle. The therapy typically involves a combination of drugs, each acting on different viral targets. These drugs include reverse transcriptase inhibitors, which prevent the reverse transcription of viral RNA into DNA; integrase inhibitors, which block the integration of viral DNA into the host genome; and protease inhibitors, which inhibit the viral protease enzyme, crucial for the maturation of new virus particles. By targeting different stages of viral replication, ART effectively reduces the viral load in the patient’s body, improving immune function and reducing the risk of HIV transmission and progression to AIDS.

Eradicating malaria poses significant challenges due to various factors. The Plasmodium parasite has shown resilience and adaptability, with some strains developing resistance to antimalarial drugs. The Anopheles mosquitoes, vectors of malaria, have also developed resistance to common insecticides used in control programmes. Additionally, malaria predominantly affects poorer regions where resources for sustained prevention and treatment are limited. Environmental and social factors, such as climate change and population movements, further complicate control efforts. While eradication is a long-term goal, it requires a coordinated global effort involving improved drug therapies, vaccine development, vector control strategies, and strong public health infrastructure.

Infectious diseases like cholera, malaria, tuberculosis, and HIV/AIDS have profound social and economic impacts. They disproportionately affect the poorest communities, where they exacerbate existing health inequities and contribute to a cycle of poverty and disease. These diseases can impede economic development due to healthcare costs and loss of workforce productivity. Socially, they can lead to stigma and discrimination, particularly in the case of HIV/AIDS, impacting mental health and social cohesion. The burden on healthcare systems is significant, often diverting resources from other vital services. Overall, these diseases represent a substantial public health challenge requiring integrated approaches to address both the biological and socio-economic factors involved.

Vibrio cholerae thrives in warm, alkaline, and saline environments, which are typical conditions in estuarine and coastal waters. The bacterium can survive in both fresh and saltwater, making it prevalent in areas with poor sanitation where drinking water is contaminated with sewage. The consumption of raw or undercooked seafood, particularly shellfish that have filtered water containing the bacteria, can also be a source of infection. Outbreaks are more common in densely populated areas with inadequate water treatment, poor sanitation, and hygiene practices. Seasonal variations also affect its prevalence, with higher incidence in warmer months due to favourable temperatures for its growth.